Use of aqueous polymer dispersions for protecting metallic surfaces against corrosion

ABSTRACT

Aqueous polymer dispersions based on copolymers of C 2  -C 14  olefins and monomers which contain acidic functional groups or are able to form them by hydrolysis, which dispersions may also contain colorants and/or corrosion inhibitors dispersed or dissolved in the polymer phase, are used for protecting metallic surfaces against corrosion.

This application is a National Stage Application of InternationalApplication Serial No. PCT/EP97/04813, filed on Sep. 4, 1997.

The present invention relates to the use of aqueous polymer dispersionsthat comprise as component I) at least one polymer and as component II)at least one colorant and/or a corrosion inhibitor, and also, ifdesired, a UV stabilizer, component II) being present almost completelydispersed or dissolved in the polymer phase, for protecting metallicsurfaces against corrosion.

Corrosion, especially in connection with metallic surfaces, is a seriousproblem. Corrosion damage, including secondary damage as a result ofcorrosion, gives rise to costs which amount to several percent of thegross national product of Germany (see Rompps Chemie-Lexikon under"Korrosion"). Because of this, a wide variety of techniques have beendeveloped for protecting metallic materials against corrosion. Examplesof these which might be mentioned include coating, plating with gold,with chromium and other metals, galvanizing, and the electrolyticzinc-plating of metallic surfaces. The skilled worker is also aware ofthe combination of various metallizing techniques with a coatingoperation. Not all coatings are suitable for protecting the basematerial against corrosion or as the metallizing layer. Some coatingmaterials, especially those applied from aqueous dispersion, oftenindeed make a direct contribution to the corrosion of the substrate.Moreover, under corrosive conditions, many coating materials give riseto decorative damage, such as embrittlement, cracking of the coatingfilm, clouding or discoloration of the coating film.

In principle, however, it should be possible to solve theabove-mentioned problems by the use of appropriate polymers as coatings.On environmental grounds, preference is given in this context to thosepolymers which are applied from aqueous dispersion to the surface thatis to be protected, thereby making it possible to avoid the use ofsolvents relative to the earlier solvent-containing coating materials. Adisadvantage that is found, however, is that emulsifiers are generallyrequired when aqueous polymer dispersions are prepared. Theseemulsifiers remain in the dispersions, with the consequence that thecoatings produced from the dispersions likewise comprise theemulsifiers. Under prolonged weathering, these emulsifiers may diffuseout of the coatings and thereby reduce the strength of the coating oreven attack the metallic surface that is to be protected.

EP-A 201 702 and U.S. Pat. No. 4,693,909 describe emulsifier-freedispersions based on ethylene-acrylic acid copolymers, which aresuitable for coating and thus for the protection of metallic surfacesagainst corrosion. Disadvantageous, however, is the fact thatdiscoloration of the metal surface may occur in the course of curing thecoating film at elevated temperature. Since the coating dispersions aregenerally colorless, the coated articles have a relatively unattractiveappearance and are therefore no longer marketable.

This problem can in principle be remedied if white or colored pigmentsare added to the dispersions. By adding corrosion-inhibiting pigments itis possible, moreover, to enhance the protective effect of the coatingsas well. Customarily, however, pigments of this kind are incorporatedinto the finished coating dispersion by means of an emulsifier, or areadded to the dispersion in the form of a ready-made pigment dispersionthat has been produced using an emulsifier. In addition to thefundamental disadvantages resulting from the use of emulsifiers, it isfound that the handling properties are impaired by the pigments. Forexample, edge coverage of the workpieces is poor when only a single coatis applied. In addition, the color effect brought about by the pigmentsare generally pale and not particularly decorative. If the amount ofemulsifier is reduced, such dispersions are generally no longer stable;if it is increased, the mechanical stability of the coating drops.Pigment-containing dispersions based on ethylene-acrylic acid copolymersare described, for example, in prior US Application No. U.S. Ser. No.08/625,151.

The prior German application P-19621037.2 describes emulsifier-freeaqueous polymer dispersions which comprise colored pigments dispersed inthe polymer phase. A proposed use is for the temporary protection ofsurfaces, for example glass, ceramic, coated metal or plastic, againstmechanical damage. A particular advantage stated for the coatingsobtainable from the polymer dispersions is that these coatings can bepeeled off in one piece, like a sheet, from the surface that is to beprotected.

It is an object of the present invention to provide aqueous polymerdispersions, containing colorants and/or corrosion inhibitors, whichinclude little or no emulsifier and which are suitable for protectingmetallic surfaces against corrosion. The coatings obtainable from thedispersions should ensure good adhesion to the metallic surfaces, highmechanical strength and good edge coverage even with a single coatingoperation.

We have found that this object can be achieved by the polymerdispersions described in P-19621037.2, which adhere very well tometallic surfaces and are suitable for long-term protection of metallicsurfaces against corrosion.

The present invention therefore provides for the use of aqueous polymerdispersions comprising as component I)

at least one polymer which includes in copolymerized form at least oneC₂ -C₁₄ -olefin (monomer a)), at least one monomer b), which iscopolymerizable with monomer a) and has at least one acidic functionalgroup and/or a functional group which is converted by hydrolysis into anacidic functional group, and, if desired, further monomers c),

and as component II)

at least one colorant and/or one corrosion inhibitor and, if desired, aUV stabilizer, component II) being almost completely dispersed ordissolved in the polymer phase,

for protecting metallic surfaces against corrosion.

The term metal surfaces hereinbelow refers to untreated metal surfacesand metal alloy surfaces, for example steel, aluminum, brass, copper,nickel, cobalt, bronze, silver, aftertreated metal and metal-alloysurfaces, for example metal-plated metals, zinc-plated metals, chromatedmetals, zinc-plated and chromated metals, and also metal surfaces onnonmetallic substrates that are obtainable by vacuum vapor deposition ofthe substrate, for example by sputtering, cathode atomization or flashevaporation.

In the text below, C₁ to C_(n) indicates the number of possible carbonatoms in a particular compound or a particular radical. C₁ -C_(n) -alkylrefers to linear or branched alkyls or 1 to n carbons, examples beingmethyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, t-butyl,n-pentyl, 2-pentyl, neopentyl, n-hexyl, 2-ethylhexyl, n-octyl, n-decylor n-dodecyl. C₅ -C₁₀ -cycloalkyl refers to cyclopentyl, cyclohexyl,cycloheptyl or cyclooctyl which is unsubstituted or substituted by 1, 2or 3 C₁ -C₄ -alkyls, preferably methyl or ethyl. Aryl is preferablyphenyl or naphthyl which is unsubstituted or substituted by 1-4 C₁ -C₄-alkyls, C₁ -C₄ -alkoxys or halogens. Aralkyls are aryls connected viaalkylenes, examples being benzyl or phenylethylene, which may also beunsubstituted or substituted.

Preferred monomers a) are C₂ -C₆ -olefins, especially ethylene, propene,1-butene, 2-butene or isobutene or mixtures thereof, preference beinggiven to mixtures containing ethylene as principal component. Withparticular preference, ethylene is used as sole monomer a).

Preferred monomers b) are monoethylenically unsaturated carboxylic acidsand dicarboxylic acids, especially aliphatic α,β-unsaturated mono- anddicarboxylic acids of 3 to 10 carbons, such as acrylic, methacrylic,crotonic, 2-ethylpropanoic, 2-propylpropanoic, 2-n-butylpropanoic,maleic, fumaric, itaconic and citraconic acids. Also suitable are themonoesters of the abovementioned dicarboxylic acids, preferably thosewith C₁ -C₁₂ -alkanols, for example mono-n-butylmaleic esters, theanhydrides of the abovementioned dicarboxylic acids, such as maleic,itaconic or citraconic anhydride, and aromatic vinyl carboxylic acids,such as 2-, 3- or 4-vinylbenzoic acid. Other preferred monomers b)comprise monoethylenically unsaturated sulfonic acids, examples beingvinylsulfonic, allylsulfonic and vinylbenzenesulfonic acid,monoethylenically unsaturated sulfinic acids, such asp-vinylbenzenesulfinic acid, monoethylenically unsaturated phosphonicacids, such as vinylphosphonic acid, and the monoesters thereof,monoethylenically unsaturated phosphoric acid monoesters, such as allylphosphate, and the alkali metal salts of the abovementioned acids andmonoesters. Particularly preferred monomers b) are acrylic acid,methacrylic acid and vinylsulfonic acid and/or their alkali metal salts.

Preferred monomers c) include, as noncrosslinking monomers c₁): theesters of monoethylenically unsaturated carboxylic acids, the amides ofmonoethylenically unsaturated carboxylic acids, for example acrylamide,methacrylamide and the N--C₁ -C₆ -alkyl- and N,N-di-C₁ -C₆ -alkylderivatives thereof,

C₁ -C₁₀ -alkyl vinyl ethers, for example methyl vinyl ether, ethyl vinylether, n-propyl vinyl ether and 2-ethylhexyl vinyl ether, diesters ofmonoethylenically unsaturated dicarboxylic acids, preferably those withC₁ -C₆ -alkanols, for example dimethyl maleate or di-n-butyl maleate,

monoethylenically unsaturated phosphoric esters, monoethylenicallyunsaturated phosphonic esters, such as di-C₁ -C₆ -alkylvinylphosphonates,

vinyl and allyl C₂ -C₁₂ -alkanoates, for example vinyl and allylacetate, vinyl and allyl propionate, vinyl and allyl butyrate, vinyl andallyl valerate, vinyl and allyl hexanoate, vinyl and allylethylhexanoate and vinyl and allyl decanoate.

Particularly preferred monomers c₁) comprise the C₁ -C₁₀ -alkyl, C₅ -C₁₀-cycloalkyl, C₆ -C₂₀ -aryl and C₇ -C₂₀ -aralkyl esters, but especiallythe C₁ -C₁₀ -alkyl esters, of the monocarboxylic acids mentioned underb). Very particular preference is given to the C₁ -C₁₀ -alkyl esters ofmethacrylic and/or acrylic acid, examples being methyl acrylate andmethacrylate, ethyl acrylate and methacrylat, n-propyl acrylate andmethacrylate, n-butyl acrylate and methacrylate, 2-butyl acrylate andmethacrylate, t-butyl acrylate and methacrylate, n-hexyl acrylate andmethacrylate, and 2-ethylhexyl acrylate and/or methacrylate.

In addition, the monomers c) also comprise crosslinking and/orcrosslinkable monomers c₂). These are polyfunctional monomers which inaddition to the ethylenically unsaturated bond include an epoxy,hydroxyl, n-alkylol or carbonyl group. Examples thereof are theN-hydroxyalkyl amides and N-alkylol amides of the abovementionedethylenically unsaturated carboxylic acids, for example2-hydroxyethyl(meth)acrylamide and N-methylol(meth)acrylamide, and alsoglycidyl acrylate and glycidyl methacrylate. Other suitable crosslinkingmonomers c₂) are those having 2 or more non-congugated ethylenicallyunsaturated bonds, such as the diesters of dihydric alcohols with theabovementioned ethylenically unsaturated monocarboxylic acids, the vinylesters or allyl esters of the ethylenically unsaturated carboxylicacids, or divinylaromatic compounds. Examples thereof are ethyleneglycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycoldiacrylate, propylene glycol diacrylate, vinyl methacrylate, vinylacrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallylfumarate, methylenebisacrylamide, cyclopentadienyl acrylate,tricyclodecenyl (meth)acrylate, divinylbenzene, divinylnaphthalene,N,N'-divinylimidazolin-2-one, triallyl phosphate or triallylcyanurate.In the preferred embodiments of the present invention, however, thepolymers contain no copolymerized crosslinking monomers.

In the particularly preferred embodiments of the present invention, thepolymers comprise as monomer a) ethylene as sole monomer and as monomerb) acrylic acid and/or methacrylic acid and also, if desired,vinylsulfonic acid and/or its alkali metal salts and, if desired, asmonomer c), one or more C₁ -C₁₀ -alkyl acrylates or methacrylates, allin copolymerized form.

In a very particularly preferred embodiment the polymers comprise thefollowing combinations of copolymerized monomers: ethylene/acrylic acid,ethylene/methacrylic acid, ethylene/acrylic acid/sodium or potassiumvinylsulfonate, ethylene/acrylic acid/n-butyl acrylate, ethylene/acrylicacid/2-ethylhexyl acrylate, ethylene/acrylic acid/n-butyl methacrylate,and ethylene/acrylic acid/2-ethylhexyl methacrylate.

The polymer dispersions employed in accordance with the inventiongenerally comprise

from 50 to 98% by weight, in particular from 60 to 90% by weight ofmonomer a),

from 2 to 50% by weight, preferably from 10 to 40% by weight of monomerb),

from 0 to 40% by weight, preferably from 0 to 30% by weight of monomerc₁), and

from 0 to 5% by weight, preferably from 0 to 1% by weight of monomer c₂)in copolymerized form.

The relative proportions of the monomers a), b), c₁) and c₂) are chosensuch that the film-forming temperature (comparable with the glasstransition temperature according to Fox: Fox et al., Bull. Am. Phys.Soc. (Ser. II) 1, 123 (1956); regarding the minimum film-formingtemperature see also Ullmanns Enzyklopadie der technischen Chemie, 4th.edition, Verlag Chemie, Weinheim (1980), Vol. 19, p. 17 ff) is below 80°C., preferably below 50° C. and, with particular preference, below 25°C.

Colorants and corrosion inhibitors used can in principle be all priorart colorants and corrosion inhibitors which can be incorporated intothe polymers, with the proviso that the stability or any other essentialproperty of the colorants or corrosion inhibitors is not adverselyaffected by the acid groups that are present in the polymer. Conversely,the colorants or corrosion inhibitors should not adversely affect thestability of the polymer dispersions and/or of the coatings producedtherewith. The colorants and the corrosion inhibitors are preferablyselected from organic pigments, inorganic pigments, organometallicpigments or other organic compounds which are insoluble in the aqueousphase.

Examples of inorganic pigments that are suitable as colorants aretitanium dioxide, Al₂ O₃, barium sulfate, strontium sulfate, zinc oxide,zinc phosphates, black iron oxide, lead chromate, strontium chromate,barium chromate, new kinds of special-effect pigments, for example TiO₂₋or Al₂ O₃ -coated mica flakes, and also metallic pigments such asaluminum powders or bronze powders.

Examples of organic pigments that are suitable as colorants comprise:

azo pigments, metal complex pigments, such as azo and azomethine metalcomplexes, isoindolinone and isoindoline pigments, phthalocyaninepigments, quinacridone pigments, perinone and perylene pigments,anthraquinone pigments, diketopyrrolopyrrole pigments, thioindigopigments, dioxazine pigments, triphenylmethane pigments, quinophthalonepigments and fluorescent pigments. A compilation of other suitablepigments is given, for example, in "The Printing Ink Manual" D. E.Bisset et al. (editors), 3rd ed, Verlag Van Nostrand Reinhold Co. Ltd,Wokingham UK, 1984, p. 209; Ullmanns Enzyklopadie der technischenChemie, 5th edition, vol. A3, pp. 144-149, A20, pp. 243-413, and H.Saechtling, Kunststoff-Taschenbuch, 21st ed., p. 40).

Suitable corrosion inhibitors comprise, in particular, inorganicpigments such as zinc phosphates, zinc borates, silicic acid orsilicates, for example calcium or strontium silicates, and also organicpigments, for example intrinsically conductive polymers such aspolypyrrol, polythiophene or polyaniline.

Suitable UV stabilizers are all inorganic or organic UV stabilizerswhich can be used for plastics, examples being substitutedbenzophenones, salicylic esters, hydroxyphenylbenzotriazoles, and thecompounds known as hindered amine light stabilizers (HALS). They aregenerally used in amounts of from 0.01 to 1% by weight, based on thepolymer.

The polymers employed in accordance with the invention and theirpreparation are known in principle to the skilled worker. They can beprepared by all common polymerization techniques, for example byemulsion polymerization (see Houben-Weyl, Methoden der organischenChemie, Volume E20/I, Makromolekylare Stoffe, Georg-Thieme-Verlag,Stuttgart, 1987), or, preferably, by continuous high-pressurepolymerization. The latter procedure is particularly advisable in thecase of the highly volatile olefins ethylene and propylene. Moreover,emulsifier-free polymer dispersions are obtained by this method.

Continuous high-pressure polymerization is also known in principle tothe skilled worker and can be carried out, for example, in the mannerdescribed in DE-A 34 20 168 and DE-A 35 12 564. The polymerizationgenerally takes place at from 150 to 300° C. and at a pressure of from1000 to 3000 bar in the presence of at least one free-radical initiator,for example a peroxo compound such as t-butyl peroxopivalate or an azocompound such as azobisisobutyronitrile. In addition to this, up to 5%by weight, based on the monomers, of regulators can be present. Examplesof suitable regulators are aliphatic aldehydes of 3 to 6 carbon atoms,especially propionaldehyde or n-butyraldehyde, aliphatic ketones of 3 to6 carbons, for example acetone or methyl ethyl ketone. In this contextit is worth noting that the α-olefins having more than 3 carbons maylikewise intervene in the polymerization as regulators. Thepolymerization conditions are adjusted such that the polymers have amelt viscosity at 120° C. of at least 1000 mm² /s as a lower limit (DFGStandard method C-IV7 (68), measured at 120° C.) and an MFI of at least1 (measured in accordance with DIN 53753 at 160° C. under a load of 325g) as upper limit.

The polymer dispersions are generally prepared by incorporating thecolorant, the corrosion inhibitor and, if used, the UV stabilizer(component II) by customary methods, in a first step, into the solidpolymer phase (component I). This can be done in a manner known per se,for example by coextrusion of the components, by continuous ordiscontinuous kneading or by stirring component II into the meltedpolymer. In this case the amount of component II is chosen such that itis preferably in the range from 0.05 to 50% by weight, in particularfrom 1 to 40% by weight and, with very particular preference, from 1.5to 30% by weight, based on the mass of polymer.

In a second step the polymers, now together with component II, areconverted into a dispersion by the customary methods. This is donepreferably in the presence of a base, examples being sodium hydroxide orpotassium hydroxide, ammonia, but preferably in the presence ofalkylamines, alkyldiamines or alkyltriamines, especially those whosealkyl radicals are substituted by hydroxyl groups in free, ethoxylatedor esterified form.

Particularly suitable amines are mono-, di- or trialkanolamines havingpreferably 2 to 6 carbon atoms in the hydroxyalkyl radical,monoalkyldialkanolamines and dialkylmonoalkanolamines having in eachcase 2 to 8 carbons in the alkyl and hydroxyalkyl radicals. The alkyl orhydroxyalkyl chains here may also include ether functions. It is ofcourse also possible to use mixtures of said bases. Examples ofparticularly preferred amines are diethanolamine, triethanolamine2-amino-2-methylpropan-1-ol, dimethylethanolamine anddiethylethanolamine, dimethylaminodiglycol, diethylaminodiglycol andalso ethylenediamine or diethylenetriamine.

The dispersions that are employed preferably comprise no emulsifier,since in general the polymers are self-emulsifying.

The polymers to which component II has been added are, for example,dispersed with stirring in an emulsifying autoclave at above the meltingpoint of the polymer, preferably at from 90 to 180° C., in particularfrom 90 to 150° C., under a pressure of between atmospheric pressure and4 bar, together with the necessary amount of water and the appropriateamount of a base, preferably an amine, diamine or triamine, and, ifdesired, with further auxiliaries. Techniques of this kind aredescribed, for example, in DE-A 35 12 564, incorporated herein in itsentirety by reference. The dispersion is then cooled, still withstirring, to room temperature. According to EP-A 359 045, likewiseincorporated in its entirety by reference, the operation of dispersioncan also be carried out in a customary extruder, preferably a twin-screwextruder, by mixing the components (polymer, water, base andauxiliaries) at from 70 to 200° C. and at a pressure of from 1 to 40bar. In this case it is possible in principle to combine theincorporation of component II into the polymer with the emulsifyingoperation.

Suitable auxiliaries, which are preferably added in amounts of from 0.5to 2% by weight, based on the overall mixture, are, in particular:

antifoams, such as ethylene oxide/propylene oxide block copolymershaving from 5 to 50 EO/PO units of fatty alcohols of 8 to 20 carbons, ofdiols or triols such as ethylene glycol, and ethylenes diamines,leveling agents, such as the potassium salt ofN-ethyl-n-perfluorooctanesulfonylglycine and Fluorad® FC 129 from 3 M,or else corrosion inhibitors, such as N-(2-ethylhexyl)succinicmonoamide, N-(2-ethylhexyl)phthalic monoamide,phenylsulfonylamidocaproic acid, diisobutenylsuccinic acid or Medialanacid.

For the novel use for protecting metallic surfaces against corrosion,the polymer dispersions obtained in this way preferably have solidscontents in the range from 5 to 40% by weight and, in particular, in therange from 10 to 35% by weight. The amount of base is in this casechosen so that at least 40%, preferably at least 50% and, in particular,at least 60% of the acid groups that are present in the polymer are inneutralized form.

The present invention additionally provides a method of protectingmetallic surfaces against corrosion using the novel polymer dispersions.This is effected by coating the metal surfaces to be protected with thepolymer dispersion. Owing to the favorable rheological properties of thedispersions it is possible to employ one of the customary techniques forthis purpose. Suitable techniques are, for example, coating with acustomary paint applicator system, single or multiple dipping of theparts that are to be coated into the polymer dispersion, sprayapplication of the polymer dispersion in one or more passes, for exampleby airless spraying using a pressurized gun, spin coating, orelectrostatic coating. This is generally followed by a drying step.Drying is done at room temperature or at elevated temperature, forexample in a stream of hot air or with the aid of infrared light. Thecoating can be applied in a single operation or else by repeatapplications with drying phases in between. The amount of dispersion perunit area is chosen so as to give, after drying, a film thickness ofpreferably less than 50 μm, particularly preferably less than 20 μm and,with very particular preference, less than 10 μm. The dried dispersionis firm to the touch after drying. An additional baking step subsequentto drying is not necessary, but may increase further the mechanicalresistance of the coating.

Through the use of the novel dispersions in accordance with the novelmethod it is possible to protect a wide variety of metal and metal-alloysurfaces against corrosion. At the same time, coloration of the polymerdispersions allows decorative surfaces in a desired color to beobtained. In this context it is found particularly advantageous thatthese properties can be attained in one operation. Moreover, thecoatings are notable for enhanced stability relative to known coatings,for example in respect of scratches or the cracking of the coating undermechanical stress.

The invention is now illustrated in more detail by way of the followingnonlimiting examples.

EXAMPLES

Starting Materials

The polymers used were prepared in accordance with Example 1 of DE-A 3512 564 by high-pressure polymerization of the monomers. The propertiesof the polymers are compiled in Table 1.

                  TABLE 1                                                         ______________________________________                                        Monomers                                                                      Polymer                      Ethylhexyl                                                                           MFI.sub.160/325                           No.     Ethylene Acrylic acid                                                                              acrylate                                                                             [g/min]                                   ______________________________________                                        1       79       21          --     10                                        2       68       16          16      8                                        3       60       20          20     11                                        ______________________________________                                    

The MFI (melt flow index) indicates the amount of polymer melt, ingrams, which is pressed through a standardized die within a defined timeat a given temperature and under a given load. It is determined inaccordance with DIN 53735. The particular index given indicates themeasurement temperature (° C.) and the load (g).

Preparation of the colored polymers (Examples 1 to 12)

The colored polymers used were prepared in a twin-screw extruder. Thiswas done by extruding the ethylene-acrylic acid copolymer No. 1 at 100°C. The respective color pigment was metered in through a side port so asto give the desired strength of color. The respective pigments andamounts are summarized in Table 2.

Heliogen® Blau K 6902 is a blue phthalocyanine pigment from BASF AG,Paliotol® Gelb K 1841 is a yellow pigment from BASF AG and Paliogen® RotK 3911 HD is a red metal-complex pigment from BASF AG.

Titanium dioxide Cl 2220 was obtained from Kronos AG

Printex® is a carbon black pigment from Degussa AG.

                  TABLE 2                                                         ______________________________________                                                                           % by                                                                          weight of                                  Example No.                                                                            Color    Pigment          pigment                                    ______________________________________                                        1        black    Printex ®    2                                          2        black    Printex ®    5                                          3        black    Printex ®    10                                         4        black    Printex ®    20                                         5        blue     Heliogen ® Blau K 6902                                                                     2                                          6        blue     Heliogen ® Blau K 6902                                                                     5                                          7        white    Titanium dioxide Cl 2220                                                                       2                                          8        white    Titanium dioxide Cl 2220                                                                       5                                          9        yellow   Paliotol ® Gelb K 1841                                                                     2                                          10       yellow   Paliotol ® Gelb K 1841                                                                     5                                          11       red      Paliogen ® Rot 3911 HD                                                                     2                                          12       red      Paliogen ® Rot 3911 HD                                                                     5                                          ______________________________________                                    

Preparation of the colored dispersion (Examples 13 to 21)

210 parts of colored polymer were stirred at 115° C. with amine andwater in a stirring vessel until after about 1 to 2 hours a uniformdispersion had formed. This dispersion was cooled with stirring andfiltered to remove coarse constituents. The respective parameters aregiven in Table 3.

                  TABLE 3                                                         ______________________________________                                                                      parts by                                                                             parts by                                 Example                                                                              Colored                weight of                                                                            weight of                                No.    polymer No.                                                                             Amine        amine  water                                    ______________________________________                                        13     2         Dimethylethanol-                                                                           36     754                                                       amine                                                        14     3         Dimethylethanol-                                                                           36     754                                                       amine                                                        15     5         Dimethylethanol-                                                                           36     754                                                       amine                                                        16     9         Dimethylethanol-                                                                           36     754                                                       amine                                                        17     11        Dimethylethanol-                                                                           36     754                                                       amine                                                        18     7         Dimethylethanol-                                                                           36     754                                                       amine                                                        19     7         2-Amino-2-methyl-                                                                          35.6   754.4                                                     propan-1-ol                                                  20     7         Diethanolamine                                                                             45.3   744.7                                    21     7         Triethanolamine                                                                            87.2   702.8                                    ______________________________________                                    

Comparison Examples 1 and 2 (corresponding to Examples 1 and 8 of U.S.Ser. No. 08/625,151).

Comparison Example 1

25% by weight of an ethylene/acrylic acid dispersion (Luwax® EAS 2 fromBASF AG) were mixed in a stirring vessel with 20% by weight of a carbonblack dispersion (Luconyl® Black 0066 from BASF AG).

Comparison Example 2

7.5% by weight of an ethylene/acrylic acid dispersion (Luwax® EAS 2 fromBASF AG) were mixed in a stirring vessel with 2.5% by weight of a waxoxidate (Luwax® OA 3 from BASF AG) and 5% by weight of a carbon blackdispersion (Luconyl® Black 0066 from BASF AG).

The following tests were used to determine the dispersion stability andthe coating properties (see Table 4).

The crosshatch test (GH) was carried out in analogy to DIN EN ISO 2409.The substrate used for the test was a freshly degreased brass plate. Thetest results were classified as follows:

0 Cut edges completely smooth; none of the squares of the crosshatchinghas flaked off.

1 Small splinters of the coating flaked off at the points where thecrosshatching lines intersect. Area which has flaked off is not greaterthan 5% of the crosshatched area.

2 The coating has flaked off along the cut edges and/or at the pointswhere the crosshatching lines intersect. Flaked off area ismarkedly >5%, but not substantially >15%.

3 The coating has flaked off along the cut edges totally, partially ortotally in wide strips, and/or some squares have flaked off totally orpartially. From 15 to 35% of the cross-hatched area is affected.

4 The coating has flaked off along the cut edges totally in broad stripsand/or some squares have flaked off totally or partially. From 35 to 65%of the crosshatched area is affected.

5 Any flaking worse than rating 4.

The dispersion stability (DS) was assessed visually on the basis of 30day old samples. The freshly prepared dispersions were for this testplaced in a 250 ml screw-top glass vessel and stored at room temperaturewithout stirring for 30 days. After this time, the dispersion stabilitywas assessed on the basis of the sediment formed and the transparency ofthe supernatant dispersion.

The color strength (F) and gloss (G) were assessed visually, on thebasis of zinc-plated and yellow-chromated steel panels which had beendipped once in the novel dispersion, in accordance with the followingscales:

Color strength

1 very good hiding--no showing through of the substrate material

2 good hiding--slight showing through of the substrate material

3 moderate hiding--moderate showing through of the substrate material

4 poor hiding--severe showing through of the substrate material

5 no hiding--the substrate material has not been hidden

Gloss

1 very good gloss--no haze evident on the coated surface

2 good gloss--slight haze evident on the coated surface

3 moderate gloss--haze evident on the coated surface

4 poor gloss--matt coated surface

The edge coverage (KB) was assessed at the edges of zinc-plated andyellow-chromated steel panels which had been dipped once in the noveldispersion, and was classified as good, acceptable or poor.

The corrosion protection was tested in analogy to DIN 50021, the saltspray test (SST). For this purpose, zinc-plated and yellow-chromatedsteel panels were coated with a film of the novel dispersion in a wetfilm thickness of 50 μm, corresponding to a dry film thickness of about10 μm, and were tested in a customary commercial salt spray chamber. Theparameter stated here is the time, in hours, until degree of corrosion 2is reached.

                  TABLE 4                                                         ______________________________________                                        Example No.                                                                           GS     DS          F    G    KB     SST                               ______________________________________                                        13      1-2    no sediment 1-2  1    good   576                               14      2      no sediment 1    1    good   528                               CE 1    3      severe sediment                                                                           1-2  3    poor   312                               CE 2    2-3    sediment    2    2-3  acceptable                                                                           408                               ______________________________________                                         135/hz                                                                   

We claim:
 1. A method of protecting metallic surfaces against corrosion,comprising:applying to a metal surface an aqueous polymer dispersionhaving an aqueous phase and polymer phase, which comprises a component(I) and a component (II), wherein component (I) comprises at least onepolymer which includes in copolymerized form at least one C₂ -C₁₄-olefin (monomer (a)), at least one monomer (b), which iscopolymerizable with monomer (a) and has at least one acidic functionalgroup and/or a functional group which is converted by hydrolysis into anacidic functional group, and, optionally, additional monomers (c), andcomponent (II) comprises at least one colorant and/or one corrosioninhibitor and, optionally, a UV stabilizer, wherein component (II) isalmost completely dispersed or dissolved in the polymer phase, andwherein the content of colorant and/or corrosion inhibitor is from 0.05to 50% by weight, based on the weight of the polymer; and drying theapplied dispersion to form a solid polymer film on the metal surface. 2.The method as claimed in claim 1, wherein monomer (b) is selected fromthe group consisting of monoethylenically unsaturated carboxylic acids,monoethylenically unsaturated dicarboxylic acids, anhydrides ofmonoethylenically unsaturated dicarboxylic acids, monoesters ofmonoethylenically unsaturated dicarboxylic acids, monoethylenicallyunsaturated sulfonic acids, monoethylenically unsaturated sulfinicacids, monoethylenically unsaturated phosphoric acids and the monoestersthereof, monoethylenically unsaturated phosphoric monoesters, and thealkali metal salts of these acids and monoesters.
 3. The method asclaimed in claim 1, wherein monomers (c) are selected from the groupconsisting of the esters of monoethylenically unsaturated carboxylicacids, amides of monoethylenically unsaturated carboxylic acids, thediesters of monoethylenically unsaturated dicarboxylic acids, C₁ -C₁₀-alkyl vinyl ethers, vinyl and allyl C₂ -C₁₂ -alkanoates,monoethylenically unsaturated phosphoric esters, monoethylenicallyunsaturated phosphonic acids (monomers c₁), and crosslinking monomers(c₂).
 4. The method as claimed in claim 3, wherein monomers (c₁) areselected from the group consisting of C₁ -C₁₀ -alkyl esters, C₅ -C₁₀-cycloalkyl esters, C₆ -C₂₀ -aryl esters and C₇ -C₂₀ -aralkyl esters ofmonoethylenically unsaturated carboxylic acids.
 5. The method as claimedin claim 1, wherein monomer (a) comprises ethylene and, optionally,propene, 1-butene, 2-butene and isobutene.
 6. The method as claimed inclaim 5, wherein the polymer comprises in copolymerized form as monomer(a) ethylene, as monomer (b) acrylic acid and/or methacrylic acid andalso, optionally, vinylsulfonic acid or one of its alkali metal saltsand, optionally, as monomer (c) C₁ -C₁₀ -alkyl acrylate and/or C₁ -C₁₀-alkyl methacrylate.
 7. The method as claimed in claim 3, wherein thepolymer comprises, in copolymerized form,from 50 to 98% by weight ofmonomer(a), from 2 to 30% by weight of monomer (b), from 0 to 48% byweight of monomer (c₁), and from 0 to 5% by weight of monomer (c₂). 8.The method as claimed in claim 1, wherein the colorant and the corrosioninhibitor are selected from the group consisting of organic pigments,inorganic pigments, organometallic pigments and other organic compoundswhich are not soluble in the aqueous phase.
 9. The method as claimed inclaim 1, wherein the polymer content of the dispersion is from 5 to 40%by weight, based on the overall weight of the dispersion.
 10. The methodas claimed in claim 1, wherein at least 40% of the acidic groups presentin the polymer are in neutralized form.
 11. The method as claimed inclaim 10, wherein the acidic groups present in the polymer areneutralized with an amine.
 12. The method as claimed in claim 1, whereinthe solid polymer film has a dry film thickness of below 20 μm.